Authors: Swej Shah; William Rossen; Karl-Heinz Wolf
Naturally found porous rocks are usually heterogeneous, and this heterogeneity is important when controlled experiments have to be considered for studying multiphase flow phenomena sensitive to homogeneity of the medium. In this study we explore methods to create synthetic nature-like porous media for flow experiments including both micro- and macro-scale heterogeneities. First, a pre-defined sintered glass core was analysed. The pre-defined properties of this core were properties derived from manufacturer specifications for filter discs, a few mm in thickness. The core, however, was several tens of centimetres in thickness and was made out of sintered pure borosilicate glass. Prior to sintering, the glass was crushed, sieved and compacted. The temperature profile of the oven used for sinteringdepended on the grain size being used. Properties of the sintered-glass porous material were evaluated using coreflood experiments and image analysis. We observe that the type of grains do not match the spatial characteristics expected in a natural porous medium; conchoidal fractured grain surfaces. Moreover, even when prepared with the utmost care, the grain frameworks do show heterogeneous characteristics, such as shrinkage fractures, extension of the matrix in circular patterns due to preparation steps, and edge effects along the walls of the enveloping glass tube.
In this first phase of our study we realized that a more natural analogue would be essential, i.e. with a known grain-size distribution, with a high sphericity and roundness. Such a selection would ensure a better understanding of the pore framework and corresponding spatial characteristics, like pore volume, pore-throat and pore-neck dimension distribution. We started with various natural materials, where grains and clays are mixed and exist in various proportions. Mineral composition of the rock sample used was quantified using XRD/XRF measurements. We propose a method where the clay phase is the sintering component for quartz grains. Special care is taken to avoid vugs and void spaces due to the passage of gases that are a product of dehydration, dehydroxylation of the clays and oxidation of the organic components. The porous medium has been compared with sintered glass using 3D computer tomography images and subsequent image analysis.
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